Left leaning internet advocacy group Public Knowledge sent a letter to the Federal Communications Commission (FCC) on Friday asking the agency to investigate data capped broadband plans, particularly as they related to iOS devices.

Last year Public Knowledge asked the FCC to investigate wireless data caps from AT&T and Verizon, and wired caps from Comcast twice last year.

"It is simply inexcusable that the Federal Communications Commission (FCC) has not even seen fit to ask wireless and landline carriers to explain why those caps are necessary, how they are set and how consumers are affected by them," said Public Knowledge President Gigi Sohn in a statement.

"Millions of consumers and at least two major publications have now discovered that the new iPads which went on sale come with a hidden cost – the caps on data usage which wireless carriers put on consumers," Sohn continued. "It's a ridiculous situation that the carriers sell millions of these devices specifically designed to view video on one hand, while they restrict the usage of their networks for video on the other."

Usage-based pricing could become a bigger issue as more customers using high definition-capable devices such as the new iPad consume more video.

We'll have to wait and see if the FCC continues to resist the calls from rights groups to take a serious look at broadband usage caps. It was one aspect of the net neutrality fight that the agency gave in on, and it seems like that decision has come back to haunt them.